(a) Field of the Invention
The present invention relates to a zoom camera with a focusing error correcting function and a control method for such a camera. More specifically, the present invention relates to a zoom camera and a control method in which upon a release switch being turned on, the zoom camera selectively corrects the position of the focal point based on moving direction of a lens barrel prior to release switch being operated.
(b) Description of the Related Art
In general, when taking a picture with a zoom camera, the user actuates a zoom switch to move the lens barrel to a telephoto position (i.e., in a telephoto direction) or to a wide-angle position (i.e., in a wide-angle direction) in order to adjust the magnification of the subject and compose a picture, and then depresses a shutter button to take a picture of the subject. As used herein, the term zoom should be understood as the operation of moving the lens in either the telephoto direction or the wide-angle direction.
When the shutter button is depressed to turn a release one-step switch to an on position (ON), a control system of the camera measures distance and brightness of the subject, and determines an auto focus (AF) step, that is, a displacement of the focus lens of the lens groups based on the measured distance of the subject in order to perform focus adjustment at the current distance of the subject. The control system then determines the desired exposure, that is, the opening rate of the shutter based on the measured distance and brightness of the subject.
Upon a release two-step switch being turned to an on position (ON), the control system moves the focus lens of the lens groups to the predetermined AF step to adjust the focus of the lens and opens the shutter based on the determined exposure in anticipation of photographing. In the zoom camera, however, the subject-distance-based AF is set based on a position for stopping the lens barrel by engagement of gears to move the lens barrel in a design basis direction of the camera. Thus there is a possible focusing error unless the lens barrel is at the design basis position during zooming, even though the focus is adjusted while the release two-step switch is ON.
More specifically, when the lens barrel is moved in reverse to the design base direction during zooming, the position and direction for engagement of the gears are varied and the lens barrel becomes out of place. This results in a focusing error even when focus adjustment is achieved based on the subject distance. The lens is therefore brought out of focus during photographing such that the camera produces an unclear image on the picture due to a focusing error.
It is an object of the present invention to solve the problem of conventional zoom cameras by providing a zoom camera capable of performing focus adjustment with accuracy in photographing, irrespective of the moving direction of the lens barrel during zooming before a release switch is operated.
To achieve this object, when the release switch is ON, a zoom camera according to an aspect of the present invention selectively performs a focusing error correcting operation based on the moving direction of the lens barrel during zooming. That is, the zoom camera performs the focusing error correcting operation by moving the lens barrel in reverse to, or in the opposite direction of, the zooming direction, if the lens barrel has been moved in reverse to, or in the opposite direction of, the design base zooming direction of the camera during a zooming operation and thus there is a possible focusing error.
In accordance with one aspect of the present invention, a zoom camera with a focusing error correcting function includes: a zoom switch for selecting a zooming operation to move a lens barrel either in a telephoto direction or in a wide-angle direction, a release switch comprising a release one-step switch and a release two-step switch sequentially actuated upon selection of a photographing operation, a distance measurer for measuring the distance of a subject from the camera, a light measurer for measuring the brightness of the subject, a lens barrel mover for moving the lens barrel to a corresponding zoom position during the zooming operation, a zoom position detector for detecting the zoom position of the moving lens barrel and for generating a corresponding lens barrel position signal based on the detected zoom position, a controller for, when the zoom switch is ON, driving the lens barrel mover to perfozooming operation, and, when the release one-step switch is ON, selectively driving the lens barrel mover based on the moving direction of the lens barrel before the release one-step switch is ON, so as to correct a focusing error, determining an exposure based on the measured distance and brightness of the subject, and generating a photographing signal to perform the photographing operation based on the determined exposure, when the release two-step switch is ON. The zoom camera also includes a photographing mechanism for opening a shutter based on the photographing signal to perform the photographing operation.
According to an aspect of the invention in a zoom camera designed to cause engagement of gears to move the lens barrel base in a design base direction including either a telephoto design base direction, i.e., from a wide-angle to a telephoto position, or in a wide-angle design base direction, i.e., from a telephoto position to wide-angle position, the controller controls the lens barrel mover to move the lens barrel in the design base direction for a predetermined time to correct the focusing error, if the lens barrel has been moved in a direction opposite to the design base direction during the zooming operation and the release one-step switch is ON. On the other hand, the controller performs no focusing error correction if the lens barrel has been moved in the design base direction during the zooming operation. Consequently, it is possible to obtain a clear image on the picture without a focusing error irrespective of the zoom moving direction of the lens barrel before the release one-step is turned ON.
During zooming, the controller may control the lens barrel mover to move the lens barrel in the wide-angle direction when the zoom switch is actuated to thereby move the lens barrel from a telephoto position to a wide-angle position, and then may stop the lens barrel from moving in the wide-angle direction upon the zoom switch being turned OFF. Alternatively, the controller may control the lens barrel mover to move the lens barrel in the telephoto direction when the zoom switch is actuated, to thereby move the lens barrel from a wide-angle position to a telephoto position, and then may stop the lens barrel from moving in the telephoto direction upon the zoom switch being turned OFF.
As a result, it may be possible to perform the zooming operation more rapidly with high zooming performance since the zooming operation is started or stopped immediately based on the on/off state of the zoom switch.
In another aspect of the present invention, a method for controlling a zoom camera with a focusing error correcting function includes determining whether a zooming operation is selected and moving a lens barrel either in a telephoto direction or a wide-angle direction, performing the zooming operation to move the lens barrel in the telephoto direction or the wide-angle direction upon selection of the zooming operation with a zoom switch turned ON, after completion of the zooming operation, determining whether a release switch is actuated to start a photographing operation, the release switch comprising a release one-step switch and a release two-step switch. The method further includes, with the release one-step switch ON, selectively performing a focusing error correction based on a moving direction of the lens barrel prior to the release one-step switch being turned on, measuring a distance of a subject from the camera and a brightness of the subject to determine an exposure, and opening a shutter based on the exposure, with the release two-step switch ON.
According to an aspect of the invention; in a method for controlling the zoom camera designed to cause engagement of gears to move the lens barrel in a design base direction including either a telephoto design base direction or a wide-angle design base direction, the performing the focusing error correction causes the lens barrel to move in the design base direction for a predetermined time to correct a focusing error if the lens barrel has been moved in direction opposite to the design base direction during the zooming operation. On the other hand, the focusing error correction is not performed if the lens barrel has been moved in the design base direction during the zooming operation.
According to yet another aspect of the invention, a controller for a zoom camera includes a mechanism for driving a lens barrel mover to move a lens barrel when a zoom switch is on to perform a zooming operation and a mechanism for selectively driving the lens barrel mover based on a moving direction of the lens barrel during the zooming operation to correct a focusing error when a release switch is on. The mechanism for selectively driving the lens barrel mover preferably is configured to drive the lens barrel mover to move the lens barrel in a direction of a design base zoom direction if the lens barrel moved in a direction opposite to the design base zoom direction during the zooming operation. The design base zooming direction preferably is one of a telephoto direction and a wide-angle direction. The mechanism for selectively driving the lens barrel mover preferably also is configured not to move the lens barrel to correct a focusing error if the lens barrel moved in the design base zoom direction during the zooming operation. The mechanism for selectively driving the lens barrel mover preferably drives the lens barrel mover for a predetermined time to move the lens barrel in the design base direction.